As part of an ongoing program of research on the physicochemical and biological properties of interacting macromolecules in solution, it is proposed that a Research Associate spend an additional year in my laboratory to continue his investigation into the interaction of chlorpromazine with microtubule subunit protein, tubulin. It is anticipated that his experiments will provide insight into the molecular mechanism of action of this tranquilizing drug. The interaction will be characterized quantitatively through the combined application of biochemical and biophysical methodology. After characterizing the inhibition of repolymerization of tubulin into microtubules, the interaction of chlorpromazine with tubulin independent of the reassembly process will be investigated using optical rotatory dispersion and circular dichroism; ultracentrifugation; and molecular sieve chromatography.